1. Field of the Invention
The present invention relates to a semiconductor laser device, and more particularly, it relates to a semiconductor laser device comprising a semiconductor laser element fixed to a base.
2. Description of the Background Art
A low-output nitride-based semiconductor laser for reproduction has recently been put into practice as the light source for the next-generation optical disk, while a high-output nitride-based semiconductor laser for high-speed recording is in the process of practicalization. In order to assemble a nitride-based semiconductor laser, a nitride-based semiconductor laser element is die-bonded to a seat of a metal stem through a submount with a conductive bonding layer of gold (Au), tin (Sn) or the like, and thereafter wire-bonded with gold. Thereafter the nitride-based semiconductor laser element is sealed with a cap transmitting a laser beam. In general, the side of the nitride-based semiconductor laser element provided with a gallium nitride substrate is die-bonded to the seat of the metal stem.
In a conventional nitride-based semiconductor laser, however, a nitride-based semiconductor layer is formed on a substrate of sapphire, silicon or silicon carbide by epitaxially growing a nitride-based semiconductor, and hence a semiconductor laser element is warped due to the differences between the thermal expansion coefficients and the lattice constants of the substrate and the nitride-based semiconductor layer.
In relation to this, a method of manufacturing a semiconductor laser device in consideration of a warp of a semiconductor laser element is known in general, as disclosed in Japanese Patent Laying-Open No. 2003-31895, for example.
The aforementioned Japanese Patent Laying-Open No. 2003-31895 proposes a method of manufacturing a semiconductor laser device by die-bonding a semiconductor light-emitting device chip to a mount member provided with a curved mount surface having a prescribed radius of curvature and a collet provided with a curved pressing surface also having the prescribed radius of curvature for pressing the die-bonded semiconductor light-emitting device chip from above. Thus, the semiconductor light-emitting device chip is fixed to the mount member in a state warped in a prescribed direction.
According to a conventional semiconductor laser device and the method of manufacturing the same disclosed in Japanese Patent Laying-Open No. 2003-31895, however, the semiconductor light-emitting device chip (semiconductor laser element) is die-bonded to the mount member (base) in the state warped in the prescribed direction with the mount member and the collet provided with the curved surfaces each having the prescribed fixed radius of curvature, and hence it is difficult to cope with dispersion in the warp of each semiconductor light-emitting device chip. If the semiconductor light-emitting device chip has a warp different from the shape of the curved surface of the mount member due to dispersion in the warp thereof, stress is disadvantageously caused in the semiconductor light-emitting device chip when the warp of the semiconductor light-emitting device chip mounted on the mount member is corrected in response to the shape of the curved surface of the mount member. Consequently, laser characteristics are deteriorated, and the semiconductor light-emitting device chip is broken. Particularly when a nitride-based semiconductor laser is formed with a high output, a warp of a device chip and dispersion in the warp are increased due to a long cavity length (length of the device chip), disadvantageously easily leading to the aforementioned problems.